Fix already-associated detection with driver-based BSS selection

Fix already-associated detection with driver-based BSS selection

wpa_s->pending_bssid is all zeros during connection attempt when
driver-based BSS selection is used. Take this into account when
determining whether new scan results should trigger a connection based
on wpa_s->current_ssid, i.e., a connection attempt with the selected
network instead of selected BSS.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>